linux-kernel - Re: [syzbot] [bluetooth?] INFO: task hung in hci_conn

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Message-ID: <4c59b146-df67-48d8-9378-3948dd6fb427@I-love.SAKURA.ne.jp>
Date: Mon, 29 Jan 2024 14:53:20 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+a984066a63e9c1e62662@...kaller.appspotmail.com>
Cc: eadavis@...com, Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bluetooth?] INFO: task hung in hci_conn_failed

On 2024/01/29 13:48, Hillf Danton wrote:
>> 3 locks held by kworker/1:2/779:
>>  #0: ffff8880b993ccd8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x29/0x130 kernel/sched/core.c:559
>>  #1: ffffc900038c7d80 ((work_completion)(&aux->work)#2){+.+.}-{0:0}, at: process_one_work+0x7eb/0x15d0 kernel/workqueue.c:2609
>>  #2: ffff888052984c80 (&aux->poke_mutex){+.+.}-{3:3}, at: __fd_array_map_delete_elem+0x125/0x2f0 kernel/bpf/arraymap.c:884
> 
> Could locking people shed any light on the failure of detecting the
> poke_mutex with rq lock held?
> 

Showing held locks (lockdep_print_held_locks()) is not a snapshot.
Synchronous printk() can make #0 already released by the moment #2 is taken.

Please consult printk() people for possibility of making printk() from
lockdep reports (and/or hung task reports) asynchronous.